Circuit arrangement for the imagedeflection and line-deflection coils of at least two cathode-ray tubes



Jan. 2, 1962 T. POORTER V 3,015,691

CIRCUIT ARRANGEMENT FOR THE IMAGE-DEFLECTION AND LINE-DEFLECTION COILS 0F AT LEAST TWO CATHODE-RAY TUBES Filed Feb. 4, 1959 2 Sheets-Sheet 1 FIG I FIG 2 INVENTOR TEUNIS POORTER BY M A AGEN Jan. 2, 1962 'r. POORTER 3,015,691

CIRCUIT ARRANGEMENT FOR THE IMAGE-DEFLECTION AND LINE-DEFLECTION cons OF AT LEAST TWO CATHODE-RAY TUBES Filed Feb. 4, 1959 2 Sheets-Sheet 2 IMPEDANCE s4 41 v 11 i 'n znn nu I FIGA i INVENTOR [Taurus POORTER United States Patent CIRCUIT ARRANGEMENT FOR THE IMAGE- DEFLECTION AND LlNE-DEFLECTION COILS OF AT LEAST TWO CATHODE-RAY TUBES Teunis Poorter, Eindhoven, Netherlands, assignor to North American Philips Company, Inc., New York, N.Y., a corporation of Delaware Filed Feb. 4, 1959, Ser. No. 791,059 Claims priority, application Netherlands Feb. 8, 1958 Claims. (Cl. 1787.5)

This invention relates to circuit arrangements for the image-deflection and line-deflection coils of at least two cathode-ray tubes, of which a plurality of the axes are located in substantially one plane, these axes or their prolongations, intersecting at substantially one point not situated in infinity, which point is located on the optical axis of the system of cathode-ray tubes, and the deflection currents being supplied from a common source.

Such circuit arrangements may be used inter alia in colouror stereo-television receivers, in which the cathode-ray tubes are picture tubes and in which the images produced by them are projected on a common surface. Said arrangements may also be used in colouror stereotelevision transmitters, in which the cathode-ray tubes are camera tubes and in which the scene to be represented is projected on their photo-sensitive screens. In the case of colour television, the number of the cathode-ray tubes is usually three, one of them being located in the optical axis of the system and the two other ones on each side of the optical axis. In the case of stereo-television, only the two tubes located outside the optical axis are usually present.

In either case, the projection results for the tubes located outside the optical axis are trapezoidally distorted. This distortion, which is naturally objectionable in all cases, may be compensated, if the plane passing through the axes of the cathode-ray tubes is parallel to the direction of the line deflection, by supplying a correcting signal, composed of a sawtooth of line frequency multiplied by a sawtooth of picture frequency, to the image-deflection coils of the tubes located outside the optical axis, and if the plane passing through the axes of the cathoderay tubes is parallel to the direction of the image deflection, by supplying a correcting signal, composed of a sawtooth of line frequency multiplied by a sawtooth of picture frequency, to the line deflection coils of the tubes located outside the optical axis. The correcting signal for one of the cathode-ray tubes, located outside the optical axis, is naturally required to be of opposite polarity to that for the other tube.

It has also been found that in said cases the linearity in the directions of the linerespectively image-deflection for the tubes located outside the optical axis is disturbed. This disturbance must also be compensated by correcting signals supplied to the linerespectively image-deflection coils. The last-mentioned correcting signals, which are of opposite polarity for the tubes located outside the optical axis, are constituted by parabolic currents having a recurrence frequency equal to the linerespectively picture-frequency, and which are supplied to the linerespectively image-deflection coils.

As previously mentioned, the invention relates to a circuit arrangement in which the deflection currents for the deflection are supplied by a common source. This affords the advantage with respect to the use of a plurality of sources that relatively independent variations in deflection currents cannot now occur.

An object of the invention is to provide a circuit arrangement in which the correcting signals may also be derived from a source common to the various cathode-ray tubes and in which the normal deflection currents and the 3,015,691 Patented Jan. 2, 1962 correcting signals may be supplied to the coils in a simple manner.

For this purpose, the circuit arrangement according to the invention is characterized in that the imagerespectively line-deflection coils are included in a bridge circuit in which the deflection coils of two cathode-ray tubes located outside the optical axis form parts of two interconnected branches and in which the deflection coils for any other cathode-ray tubes, which in this case are located in the plane of symmetry of the first-mentioned tubes, form parts of the diagonal having a common junction point with the said branches, further characteristics being that the source for the imagerespectively line-deflection is included in said diagonal and that the source producing the signal for correction of the distortion which is attributable to the non-parallelity of the axes of the firstmentioned cathode-ray tubes, is included in the other diagonal of the bridge circuit.

In order that the invention may be readily carried into effect, several embodiments will now be described in detail, by way of example, with reference to the accompanying drawings, in which:

FIG. 1 shows the arrangement of three cathode-ray tubes to which the invention is applicable;

FIGS. 2 and 3 show the non-corrected and the partly corrected projection results of the arrangement of FIG. 1;

FIGS. 4 and 5 show correcting signals;

FIGS. 6, 7 and 8 show embodiments of the circuit arrangement according to the invention;

FIG. 9 shows an arrangement of four cathode-ray tubes, and

FIG. 10 shows an embodiment of a circuit arrangement according to the invention applicable thereto.

Referring now to FIG. 1, which shows the arrangement of three cathode-ray tubes, it is assumed that these tubes are picture tubes of a colour-television receiver. The axes a, b and c of tubes 1, 2 and 3 are located in one plane, their prolongations intersecting at a point P on the optical axis b of the system, which is not located in infinity. It is also assumed that the plane passing through the axes a, b and c is parallel to the direction of the line deflection.

FIG. 2 shows the projection results of said tubes on a plane passing through P at right angles to the axis b of picture tube 2. The dimensions of the image 4 projected on the plane passing through P by the picture tube 1 are larger in the right-hand part of the plane, and smaller in the left-hand part of the plane, than the corresponding dimensions of the image 5 projected on the plane passing through P by the picture tube 2, the axis of which is at right angles to said plane. The dimensions of the image 6 projected on the plane passing through P by the picture tube 3 are, on the contrary, smaller in the right-hand part of the plane, and larger in the left-hand part of the plane, than the corresponding dimensions of the image 5.

If, in FIG. 1, the angles a and [3 enclosed by the axes a, b and c are equal, the distortions in the images 4 and 6, which, as may be seen from FIG. 2, have a trapezoidal character, are equal but of opposite polarity.

By supplying a correcting signal of parabolic shape, the recurrence frequency of which is equal to the line frequency, to the line-deflection coils of tubes 1 and 3, it may be ensured that the projection results of the various tubes are of the shape shown in FIG. 3. This figure shows that now the vertical edges of the images 4 and 6 coincide with those of image 5, which has remained undistorted. The correcting signal is also of a value such that the linearities of the images 4' and 6' have become equal to that of picture 5.

The parabolic correcting signal supplied to the line-deflection coil of tube 3 has the shape shown in FIG. 4. The

signal to be supplied to the line-deflection coil of tube 1 has opposite polarity.

In order to ensure that the three images further coincide correctly, a correcting signal having the shape of the signal shown in FIG. (in which the positive ordinate means an additional deflection upwards in the image direction) must be superimposed on the normal deflection current at the image-deflection coil of tube 3 and a correcting signal of opposite polarity must be superimposed on the normal deflection current at the image-deflection coil of tube 1. Such a signal may fundamentally be obtained by multiplication of a sawtooth signal having a recurrence frequency equal to the line-deflection frequency by a sawtooth signal having a recurrence frequency equal to the image-deflection frequency.

It should be noted that, if the cathode-ray tubes 1, 2 and 3 are picture tubes, the projections of the image to be reproduced on the various photo-sensitive screens have shapes similar to those of the images 4, 5 and 6 shown in FIG. 2. The correcting signals thus have a shape similar to that of the signals discussed in the preceding case.

FIG. 6 shows a circuit diagram of a circuit according to the invention for the arrangement shown in FIG. 1, in which the normal deflection currents and the correcting deflection currents for the various cathode-ray tubes may each be derived from a single source, so that the sources react upon one another to the least possible extent, whilst nevertheless the circuit arrangement is very simple of construction.

It will first be assumed that FIG. 6 relates to the imagedeflection coils.

In this case, 11 indicates the image-deflection coil of cathode-ray tube 1, 22 indicates the image-deflection coil of tube 2, and 33 indicates the image-deflection coil of tube 3. The impedances of said coils are supposed to be substantially equal to one another. The coils 11 and 33, constitute two interconnected branches of a bridge circuit, the other branches of which are constituted by equal impedances 7 and 8. The diagonal of the bridge circuit, which has a common junction point 10 with the branches including the coils 11 and 33, includes the deflection coil 22 of cathode-ray tube 2. Said diagonal also includes an impedance 9 which is equal to the impedances 7 and 8, this to ensure that the deflection currents supplied by a source 30 and traversing the three deflection coils 11, 22 and 33 are relatively equal. The extremities of said diagonal, the points 10 and 23, are connected to terminals 14 and 15 of the source 30, which supplies the normal image-deflection current.

The junction points 18 and 19, which determine the second diagonal of the bridge circuit, are connected to terminals 20 and 21 of a source 31, which supplies the signal for correcting the trapezoidal distortion of the images 4' and 6' produced by the tubes .1 and 3 on the plane passing through P at right angles to the axis b and hence the signal shown in FIG. 5. In view of the fact that the coils 11 and 33 are assumed to be equal and the impedances 7 and 8 are chosen to be equal, it follows therefrom that the currents originating from said source and traversing the coils 11 and 33 are of equal value but of opposite polarity, whilst current originating from the last-mentioned source does not traverse the coil 22. The result thereof is also that the current originating from the last-mentioned source cannot react upon the first-mentioned source. Conversely, the current supplied by the first-mentioned source does not cause any potential difference across the diagonal determined by the points 18 and 19, so that this current can neither react upon the last-mentioned source.

If it is assumed that the circuit arrangement of FIG. 6 relates to the line-deflection coils, the source 30 supplies the normal line-deflection current and the source 31 supplies the parabolic signal of FIG. 4, the recurrence frequency of which is equal to the line frequency.

If, in FIG. 1, the plane passing through the axes a, b

and c is parallel to the direction of the image deflection, this in contradistinction to what has been assumed hitherto, namely that this plane is parallel to the direction of the line deflection, then in the case that FIG. 6 relates to the image-deflection coils, the source 30 would have to supply the normal image-deflection currents and the source 31 a parabolic signal, the shape of which is shown in FIG. 4, but the recurrence frequency of which is equal to the picture frequency, and in the case that FIG. 6 relates to the line-deflection coils, the source 30 would have to supply the normal line-deflection currents and the source 31 the signal shown in FIG. 5.

In the circuit arrangement shown in FIG. 6, the source 30 is connected parallel to the elements included in the diagonal between the points 23 and 10. FIG. 7 shows one embodiment of the circuit arrangement according to the invention, in which the source for the normal imagerespectively line-deflection is connected in series with the elements included in said diagonal. Identical elements in FIGS. 6 and 7 are indicated correspondingly. The figure is self-explanatory, only it is necessary to make allowance for the fact that now in the diagonal between the points 23 and 10 the current supplied by source 30 is twice as great as that traversing the branches, and that the direction of the current in said diagonal is opposite to that traversing the branches.

minals to the coils associated with picture tube 2 must in this circuit be reverse to that in the circuit of FIG. 6. By connecting also an equal impedance 27 parallel to the coil 22, the current traversing coil 22 is also brought at the correct value. The resistor 9 of FIG. 7 may in this case be dispensed with.

It is to be noted that the impedance 27 may alternatively be a deflection coil of a cathode-ray tube.

FIG. 8 shows in greater detail the circuit arrangement of FIG. 6, in which it is assumed that the plane passing through the axes of the tubes is parallel to the direction of the line deflection and the coils are imagedeflection coils. Identical elements in FIGS. 6 and 8 are indicated correspondingly. In series with the coils 11, 22 and 33 there are connected inductances 41, 42 and 43, which serve to control the image linearity and resistors 51, 52 and 53 which permit of controlling the image amplitude.

The impedances 7 and 8 of FIG. 6 are consituted in FIG. 8 by the dynamic transformer impedance of a transformer 40, as seen between points 54 and 55, the primary winding of which transformer is coupled to the terminals of source 31, and by the transformer impedance, as seen between the points 55 and 56. Joints 55 and 10 are connected via a transformer 60 to the terminals of source 30. In order to neutralize as much as possible the influence of any remaining unbalance of the bridge, the source 30 is bridged by a capacitor 29.

FIG. 9 shows diagrammatically the arrangement of four cathode-ray tubes 61, 62, 63, 64. The plane passing through the axes of the tubes 61 and 62 is assumed to be parallel to the direction of the line deflection and the plane passing through the axes of the tubes 63 and 64 is assumed to be parallel to the direction of the image deflection.

The normal image-deflection current must thus be supplied to the image deflection coils of all tubes. At the image-deflection coils of tubes 61 and 62, it is furthermore necessary to superimpose upon said deflection current the correcting signals shown in FIG. 5 (naturally with opposite polarities) and to supply to the imagedeflection coils of tubes 63 and 64, as a superposition on the normal image deflection, parabolic signals (naturally likewise with opposite polarities) as shown in FIG. 4, having a recurrence frequency equal to the picture frequency.

Similarly, the normal line-deflection current must be supplied to the line-deflection coils of all tubes. Further- The latter fact is naturally not objectionable, only the connection of the termore the parabolic signal shown in FIG. 4, must be supplied as a superposition to the line-deflection coils of tubes 61 and 62 but now with a recurrence frequency equal to the line frequency, and the signal shown in FIG. 5 must be supplied as a superposition to the linedeflection coils of tubes 63 and 64.

FIG. shows a circuit arrangement according to the invention for the image-deflection coils.

71, 72, 73 and 74 are the image-deflection coils of the tubes 61, 62, 63 and 64.

The impedances of the coils 71 and 72 constitute two interconnected branches of a bridge circuit, the other branches of which are constituted by the dynamic transformer impedances of a transformer 75, as seen between points 76 and 77, and 77 and 78, respectively.

The diagonal of the bridge circuit, which has a common point 80 with the branches including the coils 71 and 72, includes the parallel combination of the coils 73 and 74. Said coils in turn constitute the branches of a bridge circuit, the two other branches of which are constituted by the dynamic transformer impedances of a transformer 81, as seen between points 82 and 83, and 83 and 84, respectively.

The points 77 and 80 are connected via a transformer 85 to the terminals of a source 90, which supplies the normal image-deflection current for the coils 71, 72, 73, 74. In proportioning the transformers 75 and 81, allowance must be made for the fact that the deflection currents in the coils 71, 72, 73 and 74 are substantially equal to one another. (In this case it is thus again assumed that these coils are relatively equal.) If necessary, additional impedances may be connected in the branches including the coils 71 and 72 and/or in the branches including the coils 73 and 74.

The primary winding of transformer 75 is connected to a source 91, which supplies the correcting signal for the 'coils 71 and 72 of the tubes 61 and 62, which signal thus has the shape shown in FIG. 5. In view of the bridge-like character of the circuit, this correcting signal does not occur in the coils 73 and 74 of the tubes 63 and 64. It will be evident that the correcting signal traverses the coils 71 and 72 with opposite polarity.

The primary winding of transformer 81 is connected to a source 92 which supplies the correcting signal for the coils 73 and 74 of the tubes 63 and 64, which signal has the shape shown in FIG. 4, and the recurrence frequency of which is equal to the picture frequency. In view of the bridge-like character of the two parts of the diagonal between points 83 and 80, which are connected in parallel for the normal deflection, said signal does not occur in the coils 71 and 72 of the tubes 61 and 62. This correcting signal also traverses the coils 73 and 74 with opposite polarity.

Also as a result of the bridge-like character of the circuit, the various signal sources do not react upon one another.

If the coils 71, 72, 73 and 74 are line-deflection coils instead of image-deflection coils, the circuit arrangement as such may be completely maintained. However, in this case, the sources 90, 91 and 92 must supply respectively the normal line-deflection currents, a parabolic signal having a recurrence frequency equal to the line frequency, and a signal as shown in FIG. 5.

What is claimed is:

l. A deflection circuit for a cathode-ray tube system of the type including a pair of cathode-ray tubes having coplanar axes intersecting at a point on the optical axis of the system, the axes of said tubes being outside of said optical axis, said circuit comprising a bridge circuit, a pair of separate deflection coil means for said tubes, said pair of deflection coil means comprising adjacent arms of said bridge circuit, a source of deflection signals for said coil means, means applying said deflection signals between diagonal junctions of said bridge circuit, a source of correction signals for correcting of distortion attributable to the non-parallel disposition of said axes, and means applying said correction signals to the remaining junctions of said bridge circuit.

2. A deflection circuit for a cathode-ray tube system of the type including first and second cathode-ray tubes having coplanar axes intersecting at a point on the optical axis of the system, the axes of said tubes being outside of said optical axis, said circuit comprising a bridge circuit, first and second deflection coils positioned to deflect the beams of said first and second cathode-ray tubes respectively, said first and second deflection coils comprising adjacent arms of said bridge circuit, first and second substantially equal impedance means comprising the remaining arms of said bridge circuit, a source of deflection signals, means applying said deflection signals between diagonal junctions of said bridge circuit, a source of correction signals for correcting distortion attributable to the non-parallel disposition of the axes of said tubes, and means applying said correction signals between the remaining junctions of said bridge circuit.

3. The circuit of claim 2, comprising a transformer having a primary and first and second secondary windings, said first and second secondary windings comprising said first and second impedance means, and means applying said correction signals to said primary winding.

4. A deflection circuit for a cathode-ray tube system of the type having first, second and third cathode-ray tubes with coplanar axes intersecting at a point on the optical axis of the system, the axis of only said second tube being on said optical axis, said circuit comprising a bridge circuit, first, second and third deflection coils for deflecting the beams of said first, second and third tubes respectively, said first and third deflection coils comprisin-g adjacent arms of said bridge circuit, said second deflection coil comprising a first diagonal of said bridge circuit connected to the junction of said first and second deflection coils, a source of deflection signals, means applying said deflection signals between said junction and the diagonally opposite junction of said bridge circuit, a source of correction signals for correcting distortion attributable to the nonparallel disposition of the axes of said tubes, and means connecting said correction source between the remaining junctions of said bridge circuit.

5. The circuit of claim 4, in which said deflection source is connected in parallel with at least a portion of said first diagonal of said bridge circuit.

6. The circuit of claim 4, in which said deflection source is connected in series with said second deflectign coil, and impedance means having substantially the same impedance as said second deflection coil is connected in parallel with said second deflection coil.

7. A deflection circuit for a cathode-ray tube system including four cathode-ray tubes symmetrically disposed and having axes intersecting at a common point, said circuit comprising a first bridge circuit, a separate deflection coil for deflecting the beam of each of said tubes, two of said deflection coils corresponding to two symmetrical said tubes comprising adjacent arms of said first bridge circuit, a source of deflecting signals, means applying said deflecting signals between the junction of said two deflection coils and the diagonally opposite junction of said bridge circuit, a second bridge circuit, the remaining said deflection coils comprising adjacent arms of said second bridge circuit, means applying said deflecting signals between the junction of said remaining deflection coils and the opposite junction of said second bridge circuit, first and second sources of correction signals for correcting distortion attributable to the non-parallel disposition of the axes of said tubes, and means connecting said first and second correction signal sources to the remaining junctions of said first and second bridge circuits respectively.

8. The circuit of claim 7, comprising first and second transformers each having a primary winding and first and second secondary windings, means connecting said first and second correcting signal sources to the primary windings of said first and second transformers respectively, the first and second secondary windings of said first and second transformers comprising the remaining arms of said first and second bridge circuits respectively.

9. A deflection circuit for a television receiver of the type having first, second and third cathode-ray tubes with coplanar axes intersecting at a point on the optical axis of the system, the axis of said second tube being on said optical axis, said circuit comprising a source of line deflection signals, a bridge circuit, first, second and third line deflection coils for said first, second and third tubes respectively, said first and third deflection coils comprising adjacent arms of said bridge circuit and said second deflection coil comprising a first diagonal of said bridge circuit between the junction of said first and second deflection coils and the opposite junction of said bridge circuit, means applying said line deflection signals across said first diagonal, means deriving parabolic correction signals from said line deflection signals of the frequency of said line deflection signals, and means applying said correction signals to the remaining junctions of said bridge circuit.

10. A deflection circuit for a television receiver of the type having first, second and third cathode-ray tubes with coplanar axes intersecting at a point on the optical axis of the system, the axis of said second tube being on said optical axis, said circuit comprising a source of line deflection signals, a source of image deflection signals, a bridge circuit, first, second and third image deflection coils for said first, second and third tubes respectively, said first and third deflection coils comprising adjacent arms of said bridge circuit and said second deflection coil comprising a first diagonal of said bridge circuit between the junction of said first and second deflection coils and the opposite junction of said bridge circuit, means applying said image deflection signals across said first diagonal, means deriving from said line deflection signals a correction signal of the frequency of said line deflection signals for correcting distortion attributable to the nonparallel disposition of the axes of said tubes, and means applying said correction signals to the remaining junctions of said bridge circuit.

References Cited in the file of this patent UNITED STATES PATENTS 2,654,854 Seright Oct. 6, 1953 2,669,900 Cherry Feb. 23, 1954 2,745,005 Lynch May 8, 1956 2,758,248 Garrett Aug. 7, 1956 2,875,273 Bailey Feb. 24, 1959 

